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Aqueous Solvent Removal of Contaminants from Soils
Published in Donald L. Wise, Debra J. Trantolo, Edward J. Cichon, Hilary I. Inyang, Ulrich Stottmeister, Remediation Engineering of Contaminated Soils, 2000
James C. O'Shaughnessy, Frederic C. Blanc
Chelating agents are helpful in removing metals from soil particles. A chelating agent is an organic that contains an anionic portion termed a ligand, which forms a bond with a metal cation. This structure is termed a metal complex and allows more metal to enter into the washwater solution. A ligand that can form two bonds to a lone metal ion is called a bidentate ligand, while ligands that can form more than two bonds to a metal ion are called polydentate ligands. A polydentate ligand which can form six bonds to a metal ion is termed a hexadentate ligand. Ethylenediaminetetraacetate (EDTA) is a hexadentate ligand which has been used as a scavenger to remove heavy metals such as lead from the human body. EDTA is relatively safe and is used in consumer food products, soaps, and cleaners. The authors have used EDTA to remove metals from contaminated soils (10-12). Naturally occurring organic ligands form organometal complexes which impede metal removal in water and wastewater treatment. Similarly, once the chelating agent metal complex has been created in the soil washing operation, treating the resulting washwaters may become more difficult, requiring extensive pH alteration to break the complex.
Titrimetric Analysis
Published in Pradyot Patnaik, Handbook of Environmental Analysis, 2017
The molecule is a hexadentate ligand because it has six donor sites: the two nitrogen atoms and the four carboxyl groups. EDTA forms chelates with all metal ions combining in a 1:1 ratio, irrespective of the charge on the metal ion. Such chelates have high stability too, because of their cage-like structures in which the ligand surrounds the metal ion, protecting the latter from solvation with solvent molecules. Another common chelate similar to EDTA is nitrilotriacetic acid (NTA), which has the following structure:
Emerging role of organic acids in leaching of valuable metals from refinery-spent hydroprocessing catalysts, and potential techno-economic challenges: A review
Published in Critical Reviews in Environmental Science and Technology, 2021
Ashish Pathak, Mari Vinoba, Richa Kothari
EDTA is an amino polycarboxylic acid that is widely used as a chelating for bindings a variety of metal cations. It is a tetracarboxylic acid, which forms strong complexes with metals through its four carboxylates groups and two amines (Mohammadi, Shalavi, & Jafarzadeh, 2013). Thus, it is a hexadentate ligand as it has six potential sites for bonding a metal ion: the four-carboxyl groups and the two amino groups, each of the latter with an unshared pair of electrons.